In drilling wells for oil and gas exploration, understanding the structure and properties of the associated geological formation provides information to aid such exploration. However, the environment in which the drilling tools operate is at significant distances below the surface. Controlled source electromagnetics (CSEM) is a technique that can be applied to evaluate resistivity variations deep underground, where the CSEM technique uses sensors that are separated by very large distances. For example, CSEM may be used to predict reservoir fluid properties and to detect resistivity of hydrocarbon deposits in marine environments. This technology may be applied to evaluate regions from near the surface to large depths below the sea floor.
In marine applications, such a sensing system typically is deployed as independent vessels or tow units, where each vessel and unit has a sensor capable of transmitting or receiving a signal. Moreover, for complete evaluation of the reservoirs that span a large area, multiple sensors and evaluation points are used. Due to the sensors being separated by large distances and disposed on different bodies, effects due to winds, tides, or waves may affect the relative orientation, signal strength, and signal timing associated with each sensor on the different vessels or tow units. Furthermore, synchronization of such sensors may be based on a time-consuming calibration scheme or a GPS (global positioning system) clock, which may not be operational under bad weather conditions. Further, the usefulness of such measurements may be related to the precision or quality of the information derived from such measurements.